The present disclosure relates to an apparatus and method for controlling a vehicle, and more particularly relates to an apparatus and method for controlling a vehicle including a torque converter with a lockup clutch.
A generally known automatic transmission mounted in a vehicle includes a torque converter coupled to an output shaft of an engine, and a transmission mechanism coupled to the output side of the torque converter and including a plurality of frictional engagement elements such as clutches and brakes, and is designed to selectively engage the frictional engagement elements to define a plurality of gears having different reduction gear ratios.
The torque converter of the automatic transmission includes a pump rotating together with a crankshaft of the engine, a turbine facing the pump and driven via a fluid by the pump, and a stator arranged inside facing portions of the pump and the turbine. The fluid circulates through the interior of a torus, comprised of the pump, the turbine, and the stator, along blades in the order of the pump, the turbine, and the stator, thereby transmitting engine output torque to the output side of the torque converter.
If the difference in rotational speed between the pump on the input side and the turbine on the output side is large, e.g., when the vehicle has just started or when the vehicle is accelerating, the stator between the pump and the turbine rectifies the flow of the fluid out of the turbine, and sends the fluid back to the pump, thereby enabling this torque converter to function to amplify torque.
It has also been known that such a torque converter is provided with a lockup clutch for directly connecting the pump and the turbine together, and the engagement of this lockup clutch eliminates the loss of torque transmitted between the pump and the turbine and improves the fuel economy performance of the engine.
In connection with this, Japanese Unexamined Patent Publication No. 2004-150531, for example, discloses a technique in which when a vehicle including a torque converter with a lockup clutch has just started, the lockup clutch is controllably moved in the direction of its engagement.
However, if, in the vehicle that has just started, the lockup clutch is controllably moved in the direction of its engagement as described above, part of the engine output torque is distributed to the lockup clutch. Thus, the engine output torque distributed to the torus decreases. If the engine output torque distributed to the torus decreases, the torque converter may fail to adequately function to amplify torque. As a result, if the vehicle that has been stopped on an uphill road and that has just started rolls down, the starting performance of the vehicle may decline because the torque converter fails to adequately function to amplify torque.
Note that the problem described above applies not only to vehicles including an automatic transmission, but also to vehicles including a continuously variable transmission or any other suitable power transmission.